Forné: I remember at the beginning of the European tour the wardrobe team came to me and said: Marc, what the fuck? These clothes are not stage tested. And I said, of course they are not tested on stage, that’s the fashion!

Horan: (laughter) It’s very real. I mean, because of what Marc says about how Sweat can be worn, now when I’m getting other things ready for her, I find myself thinking that some things seem too sweaty, or wondering if it doesn’t look like anything she wore on stage. Now I need to sculpt what the red carpet looks like and everything else outside of Sweat.

Forné: I think as long as we dress them in clothes that restrict their movements, it will be different (laughter), because with Sweat that was the most important thing: they had to be able to move.

Sure, they jump, dance, kick, etc. That’s a lot of movement.

Horan: Twenty-two shows later and Charli and I haven’t found the perfect outfit for “Track 10” yet because she’s like…I just break everything, something gets caught and I feel it break. I say, “I don’t give a damn if something breaks, that’s fine, I just need to make sure you can move.” As long as she can do whatever she wants and doesn’t edit her moves for the sake of what she’s wearing… that’s what I’m most afraid of.

What were your first reactions when you heard this tour was happening? I can’t remember the last time two pop stars performed like this.

Horan: Justin (Timberlake) and Christina (Aguilera)! I mean, I was really excited. I was a huge fan of Charli before I started working with her, and I’m a huge fan of Troye. I know both of their songs from start to finish. So I was really excited that these would be my favorite songs together, and even though they’re musically different, there’s so much overlap in the fan base. I knew it would be a huge event.

Forné: For me it was a great opportunity. I knew what we did in Europe was cool, but this would be a chance to add a lot more. I knew it would blow up a lot more. Even from the outside it seemed iconic. I saw them rehearsing in Peoria, Illinois and thought…oh my god, this is going to be crazy.